How to Maintain a Tankless Water Heater

Over time, tankless water heater systems collect minerals that erode the inside walls of the heating chambers. As a result, regular maintenance of 6-24 months is necessary. Who does the maintenance?

Well, if you’re a DIY enthusiast, flushing your tankless water heater is as easy as taking a walk in the park. Luckily, Google has lots of how-to information on this section.

However, if screwing and unscrewing things aren’t for you, you can always look for a professional. Either way, you have a role to take care of your water heating system, remember.

Below are Easy Steps on How to Do it Yourself


Start by turning off the energy source

Each tankless water heater has its source of power. For example, a gas tankless water heater uses kerosene or propane to run smoothly. On the other hand, an electric tankless heater requires electricity. All you do is cut the main gas supply or turn OFF the power source.

Close all the water valves attached to the tankless water heater

Turning off the valves helps to prevent water from trickling into the heater. It also stops heated water from coming out during the cleaning process. There are three water valves which in most cases are color-labeled. The blue valve controls the movement of cold water. The red-colored label controls the movement of hot water while the third regulates water movement from the main supply to your home.

Slowly disengage the purge port valve caps from their respective purge valves situated on both hot and cold-water valves.

Each purge valve has a small handle that resembles the letter “T.” Removing the caps helps in relieving any pressure build-up in the purge valves. In return, this prevents hot water from gushing out and probably burning your skin. Importantly, do know that there could be pressure when extracting the valve caps. Therefore, ensure that the hot water valves are securely shut off first. This will help prevent injuries from burns. You should also handle the caps carefully to avoid displacing the sealing discs from their place.

Attach a hosing line to each valve

If your heater didn’t ship with any hosing line, you could always grab 1 or 2 from the nearby store for a few dollars. The hosing line you purchase must be long enough to connect the water heater to the flushing bucket.

Connect the hoses to a sump pump that will flush and discharge water from your heater using the hot and cold water valves.

Open the port valves

You simply twist the port valves so that they are perpendicular to the hot and cold-water valves.

Add vinegar

Use 9.46 liters of unadulterated white vinegar instead of the conventional chemical solutions to clean the tankless water heater.It is safer to use organic cleaners as opposed to the chemical solutions that may be harmful to your health if ingested.

  1. Flush and drain your tankless water heater for about 45 minutes
  2. After the flush and drain process is over, close the port valves by turn, the “T” handles.
  3. Disconnect each hosing line from the water valves
  4. Seal the purge valves using the port caps- Be careful to ensure that not sealing disc is broken.

Consult the tankless water heater’s manual for instruction regarding safe ways to restart the water heater.

It’s easy, though. All you do is rotate both the hot and cold water valves such that they are positioned parallel to the main valve.

Allow air to pass through the water pipe by slowly turning on the hot water tap in the sink or shower. Allow the water to run for about 2-3 minutes until no more air bubbles are coming out of the tap.

How to flush a tankless water heater

Every tankless water heater manufacturer recommends regular maintenance including cleaning and flushing. Continuous use of hard water leaves mineral and lime deposits on the heating elements. These deposits might build up and clog the heating element thus reducing the efficiency of the water heater.

The procedure is quite the same as the one detailed above.

How to clean or descale a tankless water heater

  • Firstly, turn off the unit and cut the water supply.
  • Secondly, Open the water taps to relieve water pressure.
  • Disconnect both the outlet and inlet pipes.
  • Connect the inlet of the heater to the pump’s outlet.
  • Connect another pipe to the heater’s outlet and submerge its end into a bucket of descaling solution.
  • Take the third pipe and connect it to the pump’s inlet, and submerge its end into the bucket.
  • Ensure there is no leak.
  • Start the pump and allow it to run for some time depending on the intensity of the lime
  • After flushing the heat exchanger, run clean water through the system to clean any remaining sediments.
  • Reconnect the water heater.
  • Lastly, open all water valves and turn the power ON.

How to vent a tankless water heater

Tankless water heaters allow horizontal and vertical venting (through the roof). They require special stainless steel or PVC pipes, which are a bit pricier, compared to CPVC, PEX or Copper. However, if your budget won’t allow you to spend on PVC pipes, there are short venting runs which are quite economical and still do the trick.

To do this, move the heater to a location near the wall and direct the water lines to this point. Using special stainless steel pipes is important as they withstand any positive pressure created by the heating system.


There you have it; a simple and straightforward guide on how to maintain your tankless water heater. One more thing; always remember to pay attention to proper installation. Thereafter, this will save you from problems that might arise in the future. Finally, make the manufacturers guide your friend, most of the times it has everything you need to know.

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